The invention relates to a test phantom for a dental panoramic X-ray apparatus.
Test phantoms are used in dental panoramic X-ray radiography for an objective assesment of image quality. In conventional radiography these kind of phantoms exist for many years. The kind of information supplied therewith refers mostly to the performances of the detector, viz film, screen and developing system. In fact, manufacturers of such apparatus normally offer their own quality phantoms and criteria.
In tomography and similar techniques, however, the movement system and the generator are relevant to the overall image quality. The relevant test phantoms become more complex and expensive, due to the increasing number of parameters determining image quality such as layer depth, positioning, movement artifacts, etc.
In dental panoramic radiography some additional and particular requirements complicate the matter further. In order to be of practical advantage to a large number of potential users, including private dentists, for instance in the framework of a program for quality assurance in dental practice, a test phantom should be inexpensive and data revealed therewith should introduce an easy and unambiguous interpretation. Available test phantoms are only suitable for certain subjective checks on particular models of equipment.
Further, the subtle but fundamental question arises of what exactly is the radiological target. Dental panoramic radiology exclusively depicts teeth and jaws; in order to acertain, by a technical test phantom, how closely the radiological projection modality conforms to the organ to be depicted, it is necessary to establish an objective, i.e. mathematical, model of the organ itself.
From studies for such a model it can be concluded that:
Sex, race and age play no substantial role in determining the average contour of the dental arch at roots level. PA1 Individual deviations from the average curve are well within the range of a minimum unsharpness layer as provided by most rotational panoramic systems. PA1 The average arrangement of roots in mandible and maxilla can be described by a simple even-terms polynomial equation. PA1 To be based upon objective statistical data about the morphology of the dento-maxillo-facial complex, and to be applicable irrespective of sex, race and age. PA1 To permit quantitave evaluation of the most important parameters affecting image quality and related to the dental panoramic equipment itself. PA1 To be of simple and repeatable construction, and affordable cost, for widespread use in everyday dental practice.
It can be concluded that, in spite of considerable individual variations, it is possible to establish a meaningful model of the dentition, also including the average position and orientation of the Temporo Mandibular Joint (TMJ) condyles, on the basis of experimental statistical data available in literature.
Such a special technical test phantom would be useful for objective assesment of image quality, and of its congruency during the time, in dental panoramic radiograms, obtained from different equipment, from different units of the same type, and in different operating conditions.
Such a phantom should fulfill the following requirements:
Such a phantom should also be utilizable to check and optimize the performances of a dental X-ray panoramic apparatus during the progress of the design and application process, by optimizing the projection movement as a function of image quality obtained in the software-driven system.